Recent research has indicated that a dynamic interaction exists between opioids and feeding behavior. It has been found that 1) the administration of opioids can lead to modifications in food intake and 2) variables associated with food intake can influence the self-administration of opioids. As an example of the effects of opioids on feedig behavior, it has been shown that injections of both morphine and its antagonist, naloxone, suppress caloric intake. While both morphine and naloxone decrease total caloric intake, we have recently fond that these two drugs differentially effect intake of the three macronutrients, protein, fat and carbohydrate. In the present grant, we will determine if the selective effects of these two compounds on nutrient intake reflect general energy needs or specific nutrient requirements. Oral self-administration of morphine can lead to severe alterations in food intake. In contrast to animals drinking water, animals drinking morphine display large day to day fluctuations in total food intake and disrutptions in diurnal patterns of feeding. In the present grant, effects of oral self-administration of morphine on feeding behavior will be examined as a function of the concentration of the morphine solution. With respect to the effects of variables associated with food intake on narcotic administration, it has been recently shown that food deprivation leads to increased intakes of opioid solutions. In the present research proposal more detailed examination of the effects of food-deprivation on the oral self-administration of morphine will be conducted.